Producing purified fluid coke



United States Patent PRODUCING PURIFIED FLUID COKE C F Gray, BatonRouge, La., assignor to Esso Research and Engineering Company, acorporation of Delaware N0 Drawing. Filed May 6, 1963, Ser. No. 278,4466 Claims. (Cl. 20846) This invention relates to treating coke especiallyfluid coke particles made by the fluid coking process to render the cokesuitable for use such as in electrodes or other products 'whereimpurities'should be at a minimum in the coke particles.

Fluid coking of residual petroleum oils isbeing caring of such petroleumresidual oils contains ash constituentssuch as nickel, vanadium andother metals and sulfur which are undesirable constituents in coke andwhich are diflicultto remove because of the compact non-porous nature orstructure of the fluid coke particles. While this compact structure isdesirable from the standpoint of utilization in electrodes and the like,

it prevents removal of such contaminants by gaseous treating agents,extractants and the like. 7 v

Fluid coke particles from the fluid coking process are a different typeof petroleum coke from petroleum cokes from other processes and havedifferent characteristics. In the fluid coking process, coke particlesare circulated between the reactor whe-re heavy petroleum oil is coked,and the burner where the coke particles are reheated by burning part ofthe coke particles. The heated coke particles are then recycled to thereactor where the particles have coke deposited on them by the crackingor coking reaction and are then heated to a higher temperature in theburner and this cycle is repeated many times to form spherical cokeparticles having layers in an onion-like formation or layer-on-layerformation or a shell within a shell structure.

Each fluid coke particle has a new layer of coke added or laid down asit passes through'the reactor and at the same time ash constituents andsulfur or sulfur compounds are laid down with the coke. As the cokeparticles pass through the burner vessel they are heated and have atleast some of the volatile matter removed so that the coke particles arestronger and denser than coke obtained in other commercial cokingprocesses. The removal of contaminants or undesirable constituents fromthe inner dense layers of the fluid coke particles presents a realproblem.

According to the present invention, ash constituents or metalcontaminants are substantially removed or the amount of such ashconstituents or metal contaminants is substantially reduced in cokeparticles.

According to the present invention the amount of various ash and metalimpurities in coke can be removed or substantially reduced by firstcoking a residual petroleum oil in the presence of a caustic materialsuch as sodium carbonate, sodium hydroxide, or the like to form lo'werboiling hydrocarbons and coke. The coke containing the caustic materialis cooled and then leached with water containing nitric acid.

In the prior art it is known that coke containing a small amount ofcaustic material when leached with water alone will have some of the ashand metal contaminants removed but the extent of removal is of a muchlesser degree than that obtained with the present invention.

Various extraction steps were tried in prior processes but the removalof metals or ash such as vanadium, nickel, iron, sulfur, etc., wasnegligible. Other processes pretreated the coke as by air oxidation toimprove the porosity of the coke and while improved results wereobtained the results were not entirely satisfactory because in manyprocesses the coke product was burned.

In the present invention residual petroleum oil is coked at atemperature between about 900 F. and 980 F. About 3 to 12% by weight ofsolid sodium hydroxide per weight of residual oil was added to the oilbefore .coking. The co'ke produced was leached with a nitric acidsolution having an acid concentration between about 4 and 12 wt.percent. Preferably, hot nitric acid at or near the boiling point isused. Instead of sodium hydroxide, other caustic material such as sodiumcar bonate may be used in about 3 to 12% by weight of the sodiumcarbonate per weight of residual oil.

Instead ofadding the caustic material to the residual oil as a solid, itcan be added as a water solution and emulsified with the oil.

12% by Weight of the caustic material on the residual oil.

The fluid coke or other coke containing caustic material' was leached inone or more steps with a nitric acid solution and washed with waterafter each leaching step. At least 44% of the vanadium of the coke wasremoved'without any substantial loss of coke as is obtained in priorprocesses using a preoxidizing step, which if 'elfective, consumes about25% of the coke.

The fluid coke particles from the coking step in the presence of causticmaterial contain caustic material on the coke. The caustic material maybe sodium hydroxide or sodium carbonate either as pure or impurecompounds, that is, these compounds need not be chemically pure.

lite, corresponding to 300 micron size.

ing an aqueous sodium hydroxide solution with residual petroleum oilhaving an initial boiling point of about 950 F. to give 5 wt. percentNaOH on the residual oil.

The residual oil-sodium hydroxide emulsion was coked by being introducedinto a captive or fixed fluid bed. The fluid bed comprised 5300 grams of44-55 mesh mul- The residual oil was emulsified with concentratedaqueous NaOH solution in the weight ratio of 1 part solution to 13 partsoil to give 5% NaOH on oil. This emulsion was fed for 180 minutes with10% by weight of steam on the emulsion at a feed rate of about 28 cc. ofemulsion per minute.

A the end of 180 minutes the oil-sodium hydroxide emulsion was cut outand steam was continued at the same rate. The temperature of the fluidbed during coking was 950 F. Coke was deposited on the mulliteparticles. The mullite particles were cooled in the bed and then removedfrom the bed. Then the mullite particles were tumbled and the coke skinor layer cracked off. The coke was separated from the mullite particlesand about 660 grams of coke were produced. One portion of about poundwas leached with hot water alone, and another portion of about A poundwas leached with aqueous nitric acid solution, both at refluxconditions. The coke particles which were treated with the nitric acidsolution were leached twice with nitric acid, first with about pound ofa 15% by weight nitric acid solution at a temperature of about F. andthen washed with water at ambient temperature.

The so-treated coke particles were then again leached with about poundof a 10% by weight nitric acid solution at about 190 F. and then againwashed with A suflicient amount of a water solution of the causticmaterial is used to provide 3 to Leached With Leaehed With Hot BeforeLeaching Hot Water Nitric Acid Solution (Twice) V, p.p.m 3, 500 3,000430 Fe, p.p.m 2, 000 1, 450 1, 080 Ni, p.p.m 500 460 125 From these datait will be apparent that the present invention is extremely effective inremoving vanadium from fluid coke, as about 88% of the vanadium wasremoved. The invention is also effective in removing iron and nickel.

There was substantially no loss of coke in the leaching steps.

Additional work was done to cover petroleum oil residuum coked in thepresence of sodium carbonate as well as sodium hydroxide, lower acidconcentrations and a coke with a lower vanadium content.

In each case residual oil from Elk Basin crude, having an initialboiling point of about 850 to 1000" F., was mixed with solid sodiumhydroxide in an amount to be equal to wt. percent on the residual oilfeed, or mixed with solid sodium carbonate in an amount to be equal to 5wt. percent on the residual oil feed.

The residual oil-caustic material in each case was destructivelydistilled at 1200 F. with a slow heat-up (about 12 hours to 1200 F.) ina programmed cal-rod furnace. The coke produced was cooled and thengranulated to pass 65 mesh and refluxed with aqueous nitric acidsolution at the boiling point using about 0.9 pound of solution to 0.1pound of coke. The concentrations of the nitric acid solutions are givenin the following table. The vanadium content of the coke from thisresidual feed is about 475 p.p.m.

The results are shown in the following table.

These data show the effective removal of vanadium and provide a processfor producing a coke having less than 200 ppm. of vanadium which is themaximum concentration allowed by some aluminum companies for electrodecoke. These data also show that a single 10% HNO leach is nearlyequivalent to the successive 15% and 10% HNO leaches given in theExample I above. (72% vs. 88% vanadium removal.) Higher concentrationsof HNO than 5% by weight HNO are preferred for more effective vanadiumremoval.

In these data, sodium carbonate gave superior results to sodiumhydroxide when using 10% HNO aqueous solutions. (82% vs. 72% vanadiumremoval.

What is claimed is:

1. A process for producing fluid coke of reduced metals content whichcomprises mixing from about 3-12 Wt. percent of a caustic materialselected from the group consisting of sodium hydroxide and sodiumcarbonate with residual petroleum oil having an initial boiling pointabove about 900 F., coking the mixture in a fluid bed at a temperatureabove about 900 F. to produce coke and vaporous hydrocarbons, coolingthe coke, leaching the cooled coke with hot aqueous nitric acid havingan acid concentration between about 4 and 12 wt. percent HNO and thenwater washing the leached coke.

2. A process according to claim 1 wherein the caustic material is usedas'a solid or aqueous solution emulsified in the oil feed.

3. A process according to claim 1 wherein the coke is leached with anitric acid solution, then water washed, then treated with a nitric acidsolution again and then washed again.

4. A process according to claim 3 wherein the first nitric acidconcentration is 5 wt. percent and the concentration of the secondnitric acid solution is 10 wt. percent.

5. A process according to claim 1 wherein the temperature of the nitricacid solution is between about F. and 230 F.

6. A process according to claim 3 wherein the nitric acid treatments arecarried out under refluxing conditions.

References Cited by the Examiner UNITED STATES PATENTS 3,179,584 4/1965Hammer et al. 208-427 DELBERT E. GANTZ, Primary Examiner.

HERBERT LEVINE, Examiner.

1. A PROCESS FOR PRODUCING FLUID COKE OF REDUCED METALS CONTENT WHICHCOMPRISES MIXING FROM ABOUT 3-12 WT. PERCENT OF A CAUSTIC MATERIALSELECTED FROM THE GROUP CONSISTING OF SODIUM HYDROXIDE AND SODIUMCARBONATE WITH RESIDUAL PETROLEUM OIL HAVING AN INITIAL BOILING POINTABOVE ABOUT 900*F., COKING THE MIXTURE IN A FLUID BED AT A TEMPERATUREABOVE ABOUT 900*F. TO PRODUCE COKE AND VAPOROUS HYDROCARBONS, COOLINGTHE COKE, LEACHING THE COOLED COKE WITH HOT AQUEOUS NITRIC ACID HAVINGAN ACID CONCENTRATION BETWEEN ABOUT 4 AND 12 WT. PERCENT HNO3 AND THENWATER WASHING THE LEACHED COKE.